Aircraft refrigeration



March 7, 1950 N. E. AF KLEEN AIRCRAFT REFRIGERATION 4 Sheets-Sheet 1Filed Sept. 6, 1946 K 1 Q ..;.I

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March 7 1950 N. E. AF-KLEEN 25,499,736

AIRCRAFT REFRIGERATION Filed Sept. 6, 1946 4 Sheets-Sheet 2 INVENTOR m51%; 0;; KM BY QMtMM i/V M ATTORNEYS March 1950 N. E. AF KLEEN AIRCRAFTREFRIGERATION 4 Sheets-Sheet 3 Filed Sept. 6. 1946 ,amq wm 3 ATTORN EYS3v 1 KN 1 March 7, 1950 N. E. AF KLEEN v 2,499,735

AIRCRAFT REFRIGERATION Filed Sept. 6, 1946 4 Sheets-Sheet 4 HHHHM MZ/ZAINVENTOR GM MW l-Q Myli mv amen-3'5 ATTORNEYS Patented Mar. 7,

UNITED STATES PATENT OFFICE 2,499,736 AIRCRAFT REFRIGERATION Nils Erlandat Kleen, Stockholm, Sweden Applicatiomseptember 6, 1946, Serial No.695,144

Claims. (Cl. 62-1) This invention relates to the refrigeration andtransportation of perishable commodities or merchandise, and has for itsobject the provision of an improved method of and apparatus for therefrigeration and transportation within an aircraft of such commodities.

Perishable merchandise, especially foodstuffs, have heretofore beentransported by aircraft, and, where necessary, have been preserved byice or dry ice during transit and handling incidental to delivery to anddischarge from the aircraft. Such icing involves considerable manuallabor, and, in proportion to the amount of merchandise transported, addsa considerable amount of initial extra weight to the aircraft. Moreover,icing rarely produces the optimum conditions of temperature and humidityfor the preservation of foodstuffs, and is furthermore inflexible andnot adapted to produce the different degrees and conditions ofrefrigeration most suitable for different commodities. For example, seafood generally requires a temperature of 23 to 30 F., meats atemperature of 34 to 42 F., fresh fruits a temperature of 40 to 45 F.and fresh vegetables a temperature of 40 to 50 F. for safe preservation.

It is a common misconception that aircraft airconditioning does notrequire refrigeration simply because airplanes can be flown at asufficiently high altitude to avoid excessive ambient or outside airtemperatures. Moreover, aircraft airconditioning for passenger travel isnot suitable for perishable food preservation, the temperature being toohigh and the humidity too low. Hence, various, proposals have heretoforebeen made for refrigerating perishable air cargoes, such as vaporcompression cooling systems, air expansion turbine systems, dry ice etc.None of these expedients has attained any commercial success, and theadvantages, economies and commercial possibilities of air cargotransportation of perishable merchandise remain unavailable.

The present invention provides a simple, small, lightweightrefrigerating system with no moving parts for aircraft. In its broadaspect, the invention involves, in combination with a heatinsulatedcargo space of the aircraft, a thermal exchange system including avaporizable refrigerating medium or agent hermetically confined within aclosed circuit or tube having a liquefying zone or chamber outside thecargo space and a vaporizing zone or chamber thermally associated withthe cargo space, a cold accumulator thermally associated with thevaporizing ,zone and with the cargo space, and means associated with theliquefying zone for directing cooling air thereover while the aircraftis on the ground and in flight. The method of the invention comprisesthe steps of (1) initially refrigerating the perishable merchandise byextracting heat from the liquefying zone while the aircraft is on theground and continuing that refrigeration until sufficient cold has beenstored in the accumulator to meet the refrigerating requirements withinthe cargo space in the subsequent ascent of the aircraft to an altitudewhere the ambient air is sufiiciently low in temperature to extract heatfrom the liquefying zone, (2) continuing refrigeration within the cargospace by the cold accumulator while the aircraft is ascending, (3)maintaining refrigeration while the aircraft is aloft and restoring coldto the accumulator by extracting heat from the liquefying zone by thelow-temperature ambient air, and (4) continuing refrigeration while theaircraft is descending to ground by the cold accumulator.

The foregoing and other novel features of the invention will be bestunderstood from the following description taken in conjunction with theaccompanying drawings, in which Figs. 1, 2 and 3 are simplifieddiagrammatic sectional elevations of the thermal exchange systemutilized in the invention,

Fig. 4 is a vertical longitudinal section of an aircraft embodying theinvention,

Fig. 5 is a vertical cross section on the section line 5-5 of Fig. 4,

Fig. dis a vertical longitudinal section of a slightly modified form ofthe invention,

Fig. 7 is a vertical cross section on the section line 1'l of Fig. 6,and

Figs. 8 and 9 are diagrammatic explanatory views of thermostaticallycontrolled shutters for regulating the temperature of the cargo space.

In all the figures of the drawings the heat-insulated cargo space of theaircraft is indicated by reference numeral l0, and the thermal exchangesystem is shown as a hermetically closed tube or circuit having aliquefying (condensing) zone or chamber 1 I outside the cargo space, avaporizing zone or chamber I2 in thermal relation with the cargo space,and an intermediate connecting section I3. The evacuated tube ispartially filled with a vaporizable refrigerating medium (refrigerant),such as ammonia, the charge of refrigerant, completely liquefied, in thetube being from 10 to 20 percent of the total interior volume of thetube. The liquefying and vaporizing zones I I and ii are provided withextended heat transfer surfaces or fins M and I5, respectively. The

vaporizing zone I! is surrounded by a cold accumulator in the form of acylindrical chamber 16 spaced from but completely enclosing thevaporizing zone and partially filled with a liquid capable of freezingat temperatures around 32 F. to a solid mass, such for example as water.The exterior cylindrical surface of the chamber I6 is provided withextended heat transfer surfaces [1.

The refrigerant vaporizes in the chamber l2, thereby extracting heatfrom and cooling the surrounding cold accumulator and hence the cargospace, and the resulting vapor passes into the chamber I l where it isliquefied or condensed by a sufiiciently low-temperature atmospheresurrounding that chamber, and the liquefied refrigerant flows back intothe chamber I2. In this manner the refrigerant will circulate as long asthe temperature of the atmosphere surrounding the liquefying chamber IIis lower than the temperature of the vaporizing chamber 12. With thecold accumulator chamber l6 partly filled with water and with no othergas than water vapor present, the water will also vaporize in thechamber l6 so long as the temperature of the cargo space It is higherthan the temperature of the vaporizing chamber l2. With the liquefyingchamber ll surrounded by a sufflciently lowtemperature atmosphere, arapid heat transfer takes place between the cargo space ID and thechamber H, and the cargo space will shortly be brought down to atemperature approximating 32 F. Continued cooling of the chamber II willthen start freezing of the water in the chamber 16, and all of the watermay thus be converted to ice. This will somewhat slow down thetransmission of heat from the cargo space In to the vaporizing chamberI2. If now the temperature of the atmosphere surrounding the liquefyingchamber II should increase above the temperature of the cargo space III,the accumulated cold of the ice in the chamber 16 will hold thetemperature of the cargo space, and if this higher atmospherictemperature continues for some length of time, the ice in the chamber I6will melt, and its stored latent heat will refrigerate the cargo spaceas long as the ice melts.

By using water and not completely filling the chamber l6, no dangerouspressure will occur on either the interior or exterior wall of the rchamber. The chamber I5 is first evacuated until all air has beenremoved. It is then filled with a volume of pure water of from 80 to 90percent of the internal volume of the chamber. The evaporation,liquefaction and freezing of the water in the chamber It promotes thedesired thermal exchange and hence more rapidly cools the cargo spacethat would be the case with a non-volatile and non-freezing body ofliquid in the chamber l6, where only the specific heat of the liquidwould be available for heat exchange and cold storage. The location ofthe cold accumulator as well as the vaporizing chamber within the cargospace insures the utilization of all cold produced in the vaporizingchamber for cooling down and refrigerating the cargo space.

In the practice of the invention, in its broad aspect, the perishablemerchandise is suitably packed in the cargo space ill with the aircrafton the ground. Heat is extracted from the liquefying chamber H by anysuitable source of local artificial refrigeration, as for example byblowing refrigerated cold air over the chamber. This is continued untilthe entire body of water in the chamber l6 has been converted to ice,the acspace going too low, that is below about 32 F.

cumulator being then saturated with cold. The aircraft is then ready forflight, and the cargo space is refrigerated by the cold stored in theaccumulator 16 during the ascent of the aircraft to an altitude wherethe temperature of the ambient air is lower than 32 F., for examplearound 10 to 25 F. The low-temperature ambient air then flows around theliquefying chamber I l and maintains the refrigeration of the cargospace, and also restores the cold storage of the accumulator by freezingany water resulting from the melting of the ice during the ascent. Asthe aircraft descends for landing, the cold accumulator l6 continues therefrigeration of the cargo space from the time the aircraft leaves thelow-temperature altitude until the landing and unpacking of themerchandise from the cargo space.

Fig. 2 illustrates an embodiment of the invention in which thecirculation of the liquid medium (e. g. water) in the cold accumulatoris partly controlled. The cargo space is divided into separatecompartments Ill and [0". The vaporizing chambers l2 and I2" areconnected at their tops by a common vapor pipe 18 to the liquefyingchambers II and II" (provided with cooling fins H and I4), and theliquefied refrigerant is returned to the bottom of the chambers I2 andI2" by connecting pipes l9 and 20, respectively. The cold accumulatorchambers I6 and I6" surround the vaporizing chambers 12' and I2,respectively, and extend a substantial distance below the lower ends ofthose chambers. The chambers l6 and i6" are only partly filled withwater, so that no water is in actual contact with the chambers l2 andL2". The transmission of cold from the chambers 12' and I2" to the cargocompartments l0 and I0" is effected mainly by the vaporization of thewater by heat from the cargo compartments. The resulting water vaporcontacts the cold walls of the vaporizing chambers l2 and I2" and isthereby condensed. The contemplated heat transfer is promoted by fins orthe like l1 and I1" on the accumulator chambers l6 and [6",respectively. As the temperature of the vaporizing chambers l2 and I2",as well as of the cargo compartments I0 and It)", decreases to around 32F., the water vapor will start to freeze around the chambers l2 and I2",and the transmission of cold to the cargo compartments will be therebygreatly decreased, thus preventing the temperature of these compartmentsfalling too low, i. e. below about 32 F. Practically all of the water inthe chambers I6 and I6" may thus freeze around the chambers 12 and I2",and it may therefore be desirable to include in the chambers I6 and IS"a small amount of another volatilizable liquid of lower freezingtemperature than and immiscible with water, such for example as methylchloride, in order to provide at all times a circulating heat transfermedium. The depending legs l8 and I8" of the vapor pipe, within thecargo compartments, may be provided with cooling fins or the like 2! and22, respectively, to produce an additional refrigerating effect.Preferably, the vaporizing chambers I2 and I2" are connected near theirlower ends by a pipe 23 to assure that both chambers always have asupply of vaporizable medium, where the rate of vaporization in onechamber is slower than in the other.

In the heat-exchange systems of Fig. 1 and 2, the relatively lowheat-conductivity of ice is relied upon to prevent the temperature inthe cargo In the system shown in Fig. 3, circulation of the vaporizablerefrigerant in its hermetically closed circuit is controlled by thetemperature 01' the cargo space. In Fig. 3, similar parts are indicatedby the same reference numerals as in Fig. 1, the liquei'ying chamber IIand vaporizing chamber i2 being connected by a liquid-return tube 24 anda vapor tube 29. A closed container 28 positioned within the cargo spaceIt is connected to the vapor tube 25 by a tube 21 depending to within ashort distance of the bottom of the container 2|. A smaller vessel 28,positioned within the cargo space, is connected to the upper end of thetube 21 in open communication with that tube and the vapor tube 25.Advantageously, a second vessel 29, positioned in the ambient atmosphereof the liquefying chamber I I, is connected to the vapor tube 21. A tube30 connects the upper part 01' the container 28 with the tube 2'|. Thecontainer 28 is partly filled (to a level below the tube 30) with aliquid capable oi absorbing the refrigerant vapor. Where the refrigerantis ammonia, the liquid in the container 28 may be a solution of ammoniain water. The tube 30 permits the circulation of ammonia vapor in thecontainer 26, vapor from the pipe 21 being absorbed by the solution, andevolved vapor returning to the pipe 21 through the pipe 30.

In the simple system of Fig. 1, the pressure within the closed circuitof the refrigerating medium is that of its coldest point, which inoperation is the liquefying chamber H, and hence the pressure within thecircuit will correspond to the condensation temperature of ammoniairrespective of the temperature of the vaporizing chamber l2. In thesystem of Fig. 3, the concentration of the water-ammonia solution in thecontainer 26 is dependent upon its temperature and the pressure withinthe refrigerating circuit. By including or storing an inert gas such ashydrogen or nitrogen in the vessel 28, the pressure in the vapor side ofthe refrigerating circuit may be regulated in accordance with thetemperature of the cargo space, so that a higher pressure will prevailin the circuit at a higher temperature of the cargo space. Until thecargo space has been brought down to the contemplated low temperature,any higher temperature in that space will cause the inert gas stored inthe vessel 28 to increase the pressure in the ammonia circuit, and willalso lower the ammonia concentration of the solution in the container26, thus increasing the condensation of ammonia as well as the amount incirculation. As the cargo space reaches its contemplated lowtemperature, the inert gas pressure will decrease and the concentrationof ammonia in solution will increase, due to the lower temperaturesurrounding the vessel 28 and container 26, thus decreasing thecondensation of ammonia as well as the amount in circulation. The vessel29 contains a similar inert gas and serves, in much the same way as thevessel 28, to increase the pressure in the ammonia circuit and hence thecondensation of ammonia upon an increase in the ambient air temperaturesurrounding the liquelying chamber H.

The practical embodiment of the heat exchange system in an aircraft isdiagrammatically shown independent heat exchange systems are shown,

, hereinafter described.

chamber HA and cold accumulator ISA thermally associated with the cargocompartment or compartments A beneath the cockpit. The liquefyingchambers H are positioned on top of the aircraft, in the ambient air,within a duct or channel 3| through which the ambient air fiows when theaircraft is in flight. Shutters 32 and 33 are provided at the entranceand exit ends, respectively, of the duct for regulating the flow ofambient air through the duct, as for example as When temperatures higherthan about 32 F. are required in one or more cargo compartments, or whenthe ambient air temperature is too low, the temperature within any cargocompartment may be regulated and controlled by a combination heater andfan 34 positioned below the bottom or floor of the cargo compartment andoperatively connected to a thermostat or other temperature responsivedevice 35 positioned within the cargo compartment. When actuated byconventional thermostatically controlled means, the heater-fan 34 blowswarm air through suitable openings in the floor into the cargocompartment and thus the temperature of the compartment is automaticallycontrolled by the thermostat 35.

An enlarged and more detailed showing of the arrangement of the heatexchange system in an aircraft is illustrated in Figs. 6 and 7. Similarparts are indicated by the same reference numerals as in Figs. 4 and 5.The cargo space is divided into two forward compartments A and a largemain compartment B. The ambient air duct 3| has an air distributor inthe form of louvres 36 above the liquefying chamber assemblies foruniformly distributing the low temperature ambient air throughout theentire length or the liquefying chambers ll. Various expedients forcontrolling the temperature within individual cargo compartments areshown in Figs. 6 and 7, in addition to the thermostatically controlledheater fans 34, any or all of which may be used as desired or required.Thus, the entrance shutters 32 of the ambient air duct 3| are controlledto vary the amount of air admitted by an actuating mechanism 31operatively associated with a thermostat or other temperature responsivedevice 38 positioned within the cargo compartment B (Fig. 8). Thepivotally mounted shutters are operatlvely connected to a common linkage39 adapted to be operated (to open or close the shutters) by themechanism 31 when actuated in response to predetermined temperaturechanges of the thermostat 38. Should the temperature within the cargocompartment fall below a predetermlnedvalue, the thermostat 38 willcause the mechanism 31 and cooperating linkage 39 to operate and close,partly or completely, the shutters 32, thereby reducing or completelystopping the flow of low-temperature ambient air over the liquefyingchambers II. If, subsequently, the temperature within the cargocompartment rises above a predetermined value, the thermostat 38 willcause the mechanism 31 to open the shutters 32 and refrigeration will beresumed. If desired, the exitshutters 33 may be similarlythermostatically controlled by the temperature of the cargo compartmentto appropriately dampen the flow of low-temperature ambient air throughthe duct 3|.

The shutters 32 and 33 may also be used to reduce the air speed over thecondensing surface of the liquefying chambers. At very high air speeds,e. g. when the plane is travelling at high speed, the air friction mayunduly heat the condensing surface, and in such event the air speed maybe appropriately reduced by partially closing the shutters 32 or 33 orboth. Manipulation of the shutters for this purpose may be automaticallycontrolled by a thermostat or the like 38' (Fig. 8) thermally associatedwith the condensing surface (including the fins H) of the liquefyingchambers l l and operatively connected to the actuating mechanism 31.

In the arrangement of Figs. 6 and '7, a series of pivoted longitudinalshutters 40 is provided immediately below the cooling assemblies of thevaporizing chambers [2. Normally, these shutters are open, as shown inFig. '7, and the cargo compartment B is in open and free communicationwith the cooling assemblies. Should the temperature in the cargocompartment B fall below a predetermined value, a thermostat 4 l, withinthe cargo compartment, will cause an actuating mechanism 42 andcooperating linkage 43 to close the shutters 40 (Fig. 9), and therebyshut off the refrigerating effect of the cooling assemblies upon thecargo space. If, subsequently, refrigeration is required within thecargo compartment, the thermostat 4| will respond to that condition andwill cause the mechanism 42 and linkage 43 to open the shutters 40. Thecargo compartment A is provided with similar shutters 44 automaticallyoperated in response to predetermined temperature changes registered bya thermostat 45.

In practicing the invention in a refrigerated cargo airplane of theconstruction shown in Figs. 6 and 7 of the drawings, the perishablecommodities may be brought to the starting airport in refrigeratedtrucks or the like and will be packed in suitable cargo compartments.While on the ground at the airport, a local cooling system is used toblow cold air through the duct 31 until the cargo compartments aresufficiently refrigerated and the water in the cold accumulators l6 hasbeen converted to ice. A portable cooling system of the vapor-compressortype may advantageously be used to produce the necessary cold air, butany other cooling system, such for example as dry ice may be used. Theairplane is now ready to be flown to its destination. Should the planebe held at the airport for some considerable time, because of weather ortraflic conditions, the cold accumulator will supply refrigeration tothe cargo compartments, and after the take-off and until the planereaches an altitude at which the ambient air is cold enough forrefrigerating purposes, the cold accumulator will continue to supply thenecessary refrigeration to the cargo compartments. While in flight ataltitudes of low-temperature ambient air, refrigeration is supplied bythe flow of the ambient air through the duct 31. The louvres 36distribute the cold ambient air uniformly over the entire length of theliquefying chambers H. In addition to the automatic thermostatic controlhereinbefore described, the entrance shutters 32 and exit shutters 33may be manually or otherwise adjusted from within the cockpit or cabinof the plane to regulate the airflow through the duct 3|. While inflight, the cold accumulator will again be saturated with cold byfreezing of any water melted while standing at the airport and inascending to a low-temperature altitude. If the airplane is forced todescend before reaching its destination, the cold accumulator willsupply refrigeration to the cargo compartments to the limit of its coldstorage capacity. Simflarly, the cold accumulator will supplyrefrigeration to the cargo compartments during the descent of theairplane at its destination and until the perishable merchandise hasbeen unloaded, generally into refrigerated trucks for transportation toultimate markets.

The cold accumulator not only supplies refrigeration at periods when itis impracticable to extract heat from the liquefying chambers but servesadditionally as a temperature regulator for the cargo space to berefrigerated. Thus, when saturated with cold, the ice of the coldaccumulator acts as a heat insulator and reduces to a practical minimumany heat exchange between the cargo space and the vaporizing chambers ofthe heat transfer system. Thus, with ice as the medium of heat storage,the temperature in the cargo compartments will not fall below 32 F.

In the absence of the various temperature controls hereinbeforedescribed, the thermal exchange system of the invention tends torefrigerate the cargo space to a temperature of about 32 R, where thecold accumulator is frozen water. Lower cargo space temperatures can beobtained by protracted continuation of thermal exchange, or by thesubstitution of other bodies of liquid for pure water, as for examplesalt solutions. Cargo space temperatures higher than 32 F. can bemaintained by varying the thermal exchange between the cold accumulatorand the cargo space through manipulation of the shutters 40 (or 44) inresponse to predetermined temperature changes within the cargo space, orthrough similar manipulation of the shutters 32 or 33 or both of theambient air duct 3|, or by blowing relatively warm air into the cargospace when the temperature of the space falls below a predeterminedminimum.

I claim:

1. Apparatus for transporting perishable merchandise comprising thecombination with an aircraft having a heat-insulated cargo space, of athermal exchange system including a vaporizable refrigerating mediumwithin a hermetrically closed circuit, said circuit having a liquefyingzone in the ambient air outside the cargo space and a vaporizing zonethermally associated with the cargo space, a cold accumulator thermallyassociated with said vaporizing zone and with the cargo space, meansassociated with said liquefying zone for directing ambient cooling airover said liquefying zone while the aircraft is in flight, and meansresponsive to the occurence of a predetermined minimum temperaturewithin the cargo space for blowing relatively warm air into the space.

2. The method of refrigerating perishable merchandise within the cargospace of an aircraft while the aircraft is grounded, ascending, aloftand descending where the cargo space is adapted to be refrigerated by athermal exchange system in which a vaporizable refrigerating mediumcirculates within a hermetically sealed circuit between a liquefyingzone in the ambient air outside the cargo space and a vaporizing zonethermally associated with a cold accumulator within the cargo space,which comprises extracting heat from said liquefying zone while theaircraft is grounded to refrigerate the cargo space and store sufficientcold in the accumulator to meet the refrigerating requirements withinthe cargo space in the subsequent ascent of the aircraft through ambientair too high in temperature to extract heat from said liquefying zone,refrigerating the cargo space by the cold accumulator during the ascentof the aircraft from the ground to an altitude where the ambient airbecomes sufllciently low in temperature to extract heat from saidliquei'ying zone, extracting heat from said liquefying zone while theaircraft is aloft at said altitude by the low temperature ambient air torestore the cold extracted from said accumulator during the aircraft'sascent and to maintain refrigeration of the cargo space, andrefrigerating the cargo space by the cold accumulator during the descentof the aircraft to the ground from an altitude where the ambient airbecomes too high in temperature to extract heat from said liquefyingzone.

3. In the method of claim 2, controlling the rate of extracting heatfrom the liquefying zone while the aircraft is aloft by changes in thetemperature within the cargo space.

4. The method of claim 2 in which the thermal exchange medium of thecold accumulator is water and cold is stored in the accumulator in theform-of ice.

.5. In the method of claim 2, maintaining a predetermined temperatureabove 32 F. in the REFERENCES CITED The following references are ofrecord in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,973,116 Shutts Sept. 11, 1934FOREIGN PATENTS Number Country Date 334,696 Great Britain Sept. 11, 1930887,267 France Nov. 9, 1943 OTHER REFERENCES Mark's Handbook ForMechanical Engineers (1930), 3rd ed., McGraw-Hill, New York, N. Y.

